Soundproofing assembly and a part comprising a wall which if covered with said assembly

ABSTRACT

A soundproofing assembly intended, in particular, to soundproof a motor vehicle. The inventive assembly includes four stacked layers, consisting respectively of: a first layer having an air resistance of between 500 and 2,000 N·m−3.s; a second porous, acoustic spring-type layer having a resistivity of between 10,000 N·m−4.s and 50,000 N·m−4.s; a third viscoelastic, airtight, heavy mass-type layer having a density that is greater than or equal to 1,500 Kg/m3 and a surface density of between 0.2 Kg/m2 and 9 Kg/m2; and a fourth porous, acoustic spring-type layer having a resistivity of between 10,000 N·m−4.s and 50,000 N·m−4.s.

The invention relates to a sound-proofing assembly, in particularintended for use in a motor vehicle, as well as a component comprising awall covered with said assembly.

A large number of solutions have already been proposed to sound-proof avehicle. In particular, it is known to use a complex of the spring/masstype comprising a viscoelastic air-tight layer having a high density,forming a heavy mass, and a layer, which is porous with respect to air,forming an acoustically resilient member.

Such a solution has relatively good sound-proofing characteristics andis relatively cheap.

However, taking into consideration the proportion of thesesound-proofing members in the total mass of vehicles, manufacturers havebeen seeking to reduce the mass thereof in order to reduce the fuelconsumption of vehicles.

Other solutions have therefore been proposed, and in particular to useinstead a complex comprising two layers: one having a relatively highresistance to air passage and the other, which is porous with respect toair, forming the acoustically resilient member.

This solution consists in replacing the air-tight heavy mass with alighter layer having a resistance to air which is no longer infinite butwhich is relatively high. Such a solution, disclosed in particular inWO-A-98 18657, allows a substantial reduction in the sound-proofingmass, but it still does not provide sound-proofing of excellent quality.

In order to overcome the disadvantages of these various solutions, theobject of the invention consists in defining a new solution, optimisingthe relationship between the sound-proofing quality and the weight ofthe assembly.

To this end, the invention proposes an assembly comprising foursuperimposed layers constituted respectively by:

-   -   a first layer which has a resistance to air passage of between        500 and 2,000 N·m⁻³.s,    -   a second layer which is porous, of the acoustically resilient        member type and has a resistivity of between 10,000 N·m⁻⁴.s and        50,000 N·m⁻⁴. S, the first layer covering the second layer,    -   a third layer which is viscoelastic, air-tight, of the heavy        mass type and has a density greater than or equal to 1,500 Kg/m³        and a surface mass of between 0.2 Kg/m² and 9 Kg/m², the second        layer covering the third layer,    -   a fourth layer which is porous, of the acoustically resilient        member type and has a resistivity of between 10,000 N·m⁻⁴.s and        50,000 N·m⁴.s, the third layer covering the fourth layer.

The first pair formed by the first layer and second layer and the secondpair formed by the third layer and fourth layer defined in this mannerare relatively complementary and combine their effects to producehomogeneous results both in the field of sound-absorption and inacoustic insulation over a wide frequency range.

The applicant has established that the first pair is found to beparticularly effective in absorbing not only high frequencies (above1,000 Hz), but also mid-range frequencies (between 400 Hz and 1,000 Hz),for which the second pair is not very suitable, and that conversely thefirst pair has average acoustic insulation qualities which arecompensated for by the second pair which is relatively effective in thisrange.

Consequently, taking into consideration the various noises relating tomotor vehicles, the solution of the invention is found to beparticularly suitable for the field of sound-proofing motor vehicles, inparticular for covering the floor, the boot, the bulkhead, the parcelshelf and the door panels. As a result, it is possible to obtain areduction in weight of between approximately 15% and 35% withoutreducing the sound-proofing quality perceived in comparison with thesolutions of the prior art.

According to a complementary feature intended to optimise the absorptionof the first pair of layers, the first layer has a resistivity ofbetween 100,000 N·m⁻⁴.s and 400,000 N·m ⁻⁴.s and/or of between 3 and 20times the resistivity of the second layer.

By way of information, it is specified that the resistance of a layer toair passage is equal to the product of the resistivity of a layermultiplied by the thickness thereof.

According to another advantageous feature, according to the invention,the fourth layer has a Young's modulus which is at least two times lessthan the Young's modulus of the second layer.

In this manner, it is possible to reduce the risk that a phenomenon ofinterference (frequency coincidence) is produced between the two pairsof layers, which further improves the sound-proofing of the solutionaccording to the invention.

The invention further relates to a component comprising, in addition tothe assembly, a rigid wall, said assembly at least partially coveringsaid wall and, among said four superimposed layers, the fourth layerbeing the layer nearest the wall and the first layer being the layerfurthest away from said wall.

The invention will be appreciated even more clearly from the descriptionbelow which is given with reference to the appended drawings, in which:

FIG. 1 is a cross-section of an assembly according to the invention,

FIG. 2 is a cross-section of a variant of the assembly of FIG. 1.

FIG. 1 illustrates a component 1 comprising a rigid wall and a flexibleassembly 10. Said assembly 10 comprises a first layer 2, a secondflexible layer 4, a third flexible layer 6 and a fourth flexible layer 8which are superimposed and which cover a substantially rigid wall 17, towhich it is fixed. The component 1 delimits a space 15, such as avehicle passenger compartment, to be sound-proofed.

The first layer 2 and the second layer 4 are permeable to air, whereasthe third layer 6 is impermeable to air. Furthermore, the first layer 2has a resistance to air passage which is not infinite but which isnevertheless high. In particular, the first layer 2 has a resistivitygreater than that of the second layer 4.

In general terms, the third layer 6 and the fourth layer 8 deal with thenoise transmitted via solid means and noise transmitted through the airradiated by the wall 17 in order to insulate said wall of the passengercompartment 15. The residual sound waves which are present in thepassenger compartment 15 pass in part through the layer 2, then into thelayer 4, which forms an acoustically resilient member, where they areabsorbed, the viscoelastic, mechanically inert layer 6, which forms aheavy mass and which is supported by the layer 8, also forming anacoustically resilient member which defines a barrier to the soundwaves.

Of course, this presentation is simplistic. However, it illustrates theprincipal functions carried out by each of the layers.

In this case, the first layer 2 has a substantially uniform composition,in particular in terms of resistivity, over the entire thickness thereofand further constitutes the trim layer of the component 1. It has athickness greater than or equal to 4 millimetres, advantageously ofbetween 5 and 10 millimetres.

In particular, it can be constituted by glass, cotton or syntheticfibres (polyester, polypropylene, polyamide, acrylic) and polypropylene.By way of a variant, it can also be constituted by a compacted non-wovenfabric, a needled fabric, or the like, coated with latex. It is alsopossible to cover the first layer 2 with a trim layer, whose resistanceto air passage is negligible in relation to that of the first layer.This is the case with some velours and some floor carpets.

The second layer and the fourth layer are each advantageouslyconstituted by thermoplastic foam or felt. They can both be producedfrom the same material, but that is not necessary. Their density isadvantageously between 15 Kg/m³ and 100 Kg/m³. Their porosity(proportion of air confined for a given volume) is advantageouslygreater than 0.9 and preferably greater than 0.95. Each of the layersadvantageously has a thickness of between 5 millimetres and 20millimetres.

The heavy mass 6 advantageously comprises a thermoplastic material ofthe polyolefin type (ethylene vinyl acetate, polythene, ethylenepropylene diene monomer) and incorporates waste products of the bitumen,chalk and/or barium sulphate type, permitting a high density at lowcost. Its Young's modulus is less than 1,000 MPa and it has a densitygreater than or equal to 1,500 Kg/m³, preferably greater than or equalto 2,000 Kg/m³, a surface mass of between 0.2 Kg/m² and 9 Kg/m² andadvantageously a thickness of between 0.1 millimetres and 5 millimetres.

The thickness of the assembly 10 is advantageously between 15millimetres and 50 millimetres.

The connection between the layers is produced according to conventionaltechniques, in particular by thermo-adhesive bonding.

FIG. 2 illustrates a component 11 which differs substantially from thecomponent 1 illustrated in FIG. 1 in that it comprises an assembly 20which differs from the assembly 10 in that the first layer 2 has beenreplaced with a first layer 12 comprising two superimposed portions 12′,12″. As illustrated by way of example, the portion 12′ could beconstituted by a carpet support (needled fabric coated with latex bycomplete immersion, for example), that is to say, a trim layer having anon-negligible resistance to air passage, and the portion 12″ havingcompressed fibres (for example, compressed felt).

Naturally, the invention is in no way limited to the embodimentdescribed above by way of non-limiting example. In this manner, thefirst layer 2, 12 could comprise more than two superimposed portions.

1-8. (canceled)
 9. Assembly for sound-proofing in particular a motorvehicle, comprising four superimposed layers constituted respectivelyby: a first layer which has a resistance to air passage of between 500and 2,000 N·m⁻³.s, a second layer which is porous, of the acousticallyresilient member type and has a resistivity of between 10,000 N·m⁻⁴.sand 50,000 N·m ⁻⁴.s, the first layer covering the second layer, a thirdlayer which is viscoelastic, air-tight, of the heavy mass type and has adensity greater than or equal to 1,500 Kg/m³ and a surface mass ofbetween 0.2 Kg/m² and 9 Kg/m², the second layer covering the thirdlayer, a fourth layer which is porous, of the acoustically resilientmember type and has a resistivity of between 10,000 N·m ⁻⁴.s and 50,000N·m⁻⁴.s, the third layer covering the fourth layer.
 10. Assemblyaccording to claim 9, wherein the first layer has a resistivity ofbetween 100,000 N·m⁻⁴.s and 400,000 N·m⁻⁴.s.
 11. Assembly according toclaim 9, wherein the first layer has a resistivity of between 3 and 20times the resistivity of the second layer.
 12. Assembly according toclaim 9, wherein the third layer has a Young's modulus of less than1,000 MPa and a density of greater than or equal to 2,000 Kg/m³. 13.Assembly according to claim 9, wherein the fourth layer has a Young'smodulus which is at least two times less than the Young's modulus of thesecond layer.
 14. Assembly according to claim 9, wherein the secondlayer and the fourth layer are constituted by thermoplastic foam and/orfelt and have a density of between 15 Kg/m³ and 100 Kg/m³.
 15. Assemblyaccording to claim 9, wherein the third layer comprises a thermoplasticmaterial of the polyolefin type and incorporates waste products of thebitumen, chalk and/or barium sulphate type.
 16. Component comprising arigid wall and an assembly according to claim 9, wherein said assemblyat least partially covers said wall and, among said four superimposedlayers, the fourth layer is the layer nearest the wall and the firstlayer is the layer furthest away from said wall.